To date, over one million cataract surgeries are performed annually in the United States, in which the anterior lens capsule must be opened to gain access to the lens nucleus and allow removal of degenerated cortical material. It is necessary to create a relatively large circular opening in the lens capsule in order to enter the lens interior and to withdraw matter from inside. Formation of this opening is known as a capsulotomy. It is important that the opening has smooth edges and is tear resistant so that the lens contents can be easily removed through the opening. The lens opening is usually on the order of 5-7 millimeters in diameter, though this may vary.
Currently, two techniques for anterior capsulotomy are widely used: the “can-opener” technique and capsulorrhexis. In can-opener capsulotomy, a small incision in the sclera or peripheral cornea is performed, then a cystotome, knife, or needle is inserted through the incision and small connecting tears are made in the anterior lens capsule in a circular pattern. After a complete circle has been made by connecting the tears, a circular piece of the anterior capsule is grasped with forceps and torn away along the perforations. Unfortunately, when opening the capsule with numerous small capsular tears, the small tags that remain become a focal area of least resistance and can lead to tears, which extend radially and posteriorly to the posterior capsule. The detrimental result is a loss of structural stability of the capsule and an increased likelihood of vitreous entry into the anterior chamber.
Capsulorrhexis denotes a circular central opening in the anterior capsule. This continuous opening eliminates the residual tags common with the can-opener technique described above. In capsulorrhexis, a capsular incision is made with a cystotome, and this incision is coaxed to form a circular shape by pushing the leading edge of the freshly tearing capsule with the cystotome in a non-cutting fashion or by grasping the leading edge with forceps. This procedure is challenging for the surgeon to control. The tearing motion can lead to an undesirable tear toward the equator and the posterior capsule, and the size of the opening is difficult to dictate. Capsulorrhexis requires a significant amount of skill and experience and to consistently obtain successful results.
Opening the anterior capsule via either of the described techniques of anterior capsulotomy is a delicate procedure and is widely considered to be one of the most difficult steps in cataract surgery. A poorly performed anterior capsulotomy significantly hinders the subsequent surgical steps and increases the probability of operative complications. Complications resulting from a poor capsulotomy include zonular stress with subsequent breakage of the posterior capsule, vitreous loss, and large capsular tags preventing efficient lens removal. A poor capsulotomy also prevents placement of an intraocular lens in the capsular bag) due to ill-defined capsular structures. The operative time is lengthened and patient discomfort can be increased, along with the risk of postoperative complications and decreased visual acuity results.
With either of the above-described techniques for anterior capsulotomy, the size or position of the capsular opening is often not ideal. The location, size, and configuration of the incision have important consequences. For example, an overly small capsular opening can impair the safe removal of the lens nucleus and cortex and prevent proper intraocular lens insertion into the lens capsule. In addition, a small or eccentric capsular opening places excessive stress on the lens capsule during surgery, placing the eye at risk for zonular and capsular breakage.
Certain devices have been proposed to overcome the problems associated with D conventional anterior capsulotomy techniques. For example, U.S. Pat. No. 4,766,897 issued to Smirmaul, and U.S. Pat. Nos. 5,269,787 and 5,873,883 issued to Cozean Jr. et al. each disclose instruments that include circular cutting members for incising the anterior capsule. However, use of such devices in small incision cataract surgery is limited due to their size. Specifically, the anterior lens capsule of the eye is shielded by the cornea and sclera, such that a passage wound must be cut in the corneal or scleral tissue before any surgical apparatus can reach the anterior capsule. It is desirable to limit the width of the passage wound incised on the corneal tissue, preferably to 1-3 millimeters. A small wound decreases the scope of the surgical closing procedures, promotes rapid healing, minimizes astigmatism, reduces potential infections, and offers rapid visual rehabilitation. Therefore, the instrumentation employed in cataract surgery should be capable of passing through a small wound. Prior art cutting members cannot be passed through a small corneal incision of 1-3 mm.
Burning tools exist in which heat is concentrated at the tip, and the tip is made to contact and burn a surgical site. In use of such burning tools for cataract surgery, an incision is made in the cornea, and the tip of tool is inserted through the incision and brought into contact with the capsule, where it is activated to sear through the capsule. The use of prior art burning tools is restricted by the small size of the incision, as previously mentioned, which hampers introduction of a large tip having a circular shape of the appropriate size of the desired seared area.
International application PCT/IL05/000461 by the Applicants describes a burning ring present at an oblique angle on the end of a narrow-diameter shaft. The burning ring can therefore be introduced through a small incision, and the oblique angle grants a relatively large elliptical burn, with the largest axis of the burn being larger than the diameter of the shaft.
U.S. Pat. No. 6,066,138 to Sheffer et al. describes a searing cautery that is retractable from within a handle, so that the cautery can be extended to its final size after insertion through the corneal incision. The Sheffer patent suffers from the disadvantage that the burning ring does not close a complete circle, as apparent in FIG. 1b, with the area near the handle not being seared. Therefore, it is still necessary to grasp that remaining area with a forceps, and form a tear that is difficult to control. Additionally, since the searing ring is formed from a single metal wire extending substantially into the depths of the handle, when the wire is heated electrically, it is difficult to insulate the tool and prevent heating in unwanted areas. Searing could accidentally occur in other portions of the eye adjacent to the lens, since the handle of the tool could heat, and since the tool needs to be inserted considerably into the eye.
Other burning tools exist which have a small diameter tip, which is inserted through the incision, and used to burn a series of holes in the capsule, arranged in a ring, which is then grasped with forceps and torn into a circular opening. It is difficult to manipulate the burning tool to form a series of burns that are reliably ring-shaped and are present at the desired location, and form a ring of the desired size. It would be desirable to have a burning tool, which could be inserted through a small diameter incision in the cornea, yet could easily be used to form a large diameter ring-shaped opening in the capsule.
Thus, the need exists for a surgical tool capable of reliably performing a uniform circular-shaped opening in the capsule.
Additionally, in cataract surgery, the procedure is usually complicated by the need for multiple instruments: a cutting tool, an air pressure inlet, a water pressure inlet, and related surgical and electrical equipment. It would be useful to simplify such surgical procedures by providing a combination tool that concentrates heat on the surgical site and which is constructed so as to be convenient to handle and which can be used for providing both regulated heating and airflow pressure directed to a surgical site.
Thus, there is a need for a tool for forming a capsulotomy opening of approximately 5-7 millimeters in the lens capsule, the opening being resistant to manipulation. The tool should be able to pass through a relatively small corneal incision, i.e., on the order of 1-2 millimeters.